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Measuring a woman's breast size at age 20 may help predict whether she will develop diabetes in middle age, according to new Canadian research.
The study, published in today's edition of the Canadian Medical Association Journal, suggests that women with a bra cup size of D or larger are almost five times more likely to develop diabetes than women with an A cup.
Even after adjusting for a number of other factors that influence the risk of diabetes, such as obesity, diet, smoking and family history, the D cup women were still 68 per cent more likely to develop diabetes than women with an A cup. (Women with B and C cup sizes - the most common - saw their risk increase concomitant to cup size.)
Joel Ray, a clinician-scientist in the department of obstetrics and gynecology at St. Michael's Hospital in Toronto, said the findings are not a complete surprise, but open up some intriguing avenues for further research.
Obesity is a key risk factor for diabetes and, because breasts are principally composed of fat, women who are overweight or obese tend to have larger cup sizes.
However, the research shows that cup size is not directly correlated to body mass index, or BMI (an approximation of body fat). This raises the intriguing possibility that fat that accumulates in the breast may, like fat that accumulates in the belly, be a sort of fat-producing factory that strongly influences insulin resistance, the underlying cause of diabetes.
In fact, the research suggests that a "woman's breast size in late adolescence reflects her predisposition to insulin resistance and Type 2 diabetes" that is independent of BMI, Dr. Ray said.
If that is true, doctors will likely measure breast size the way they do belly size and view it as a red flag for diabetes and heart disease.
Dr. Ray stressed, however, that the research is preliminary and should not be acted upon at this time.
"What should women and their caregivers do with this information? Absolutely nothing," the researcher said.
More specifically, Dr. Ray said women should not think that breast reduction surgery may reduce their risk of diabetes, though he intends to study that question.Alexander Sorisky, a senior scientist in the chronic disease program of the Ottawa Health Research Institute, offered up a similar analysis.
He said that breast size may eventually prove to be a "new anatomic predictor" of Type 2 diabetes but "it's too early to tell."
Data for the new research were derived from the Nurses Health Study II, a massive research project that has been tracking the health of a large cohort of nurses in 14 U.S. states since 1989.
There were a total of 92,106 participants in the study examining the link between breast size and diabetes. During the period from 1993 to 2003, a total of 1,844 of the nurses developed the disease.
Dr. Ray and his colleagues found that the larger their bra cup size at age 20, the more likely they were to develop diabetes.
(Bra cup size is traditionally determined by measuring the horizontal chest circumference just under the breasts, adding five inches and subtracting the total from the circumference at the fullest part of the breasts. A net difference of one inch is equivalent to an A cup, and four inches is a D cup. Cup size also provides a reasonable approximation of breast volume and hence amount of fat.)
The proportion of participants with a family history of diabetes was higher among women with larger cup sizes than those with smaller cup sizes. The larger-breasted women were also more likely to have smoked.
The women with large bra cup sizes at age 20 recalled being slightly heavier at ages 5 and 10 than their less-busty counterparts.
Women with a D cup size were also younger at menarche (first menstrual period), by about five months on average, compared with women with an A cup.
Dr. Ray said this is important because the first sign of puberty in girls is the development of breast buds and fatty breast tissue.
Breast tissue is extremely hormonally responsive and insulin is a hormone. "Puberty is a definite state of insulin resistance, just as is pregnancy," Dr. Ray said.
He speculated that girls who enter puberty earlier - as obese girls are known to do - may have more pronounced development of the breasts and hence greater insulin resistance and a predisposition to diabetes.
About two million Canadians suffer from diabetes, according to the Canadian Diabetes Association. There are three distinct forms of diabetes: gestational diabetes is a temporary condition that occurs during pregnancy; Type 1 diabetes, usually diagnosed in children, occurs when the pancreas is unable to produce insulin; Type 2 diabetes, which accounts for 90 per cent of cases, occurs when the pancreas does not produce enough insulin or the body does not effectively use the insulin it produces.
Risk factors for diabetes
Weight
A body mass index (an approximation of body fat) greater than 27 puts a person at an elevated risk of developing Type 2 diabetes. (A BMI of 25 or more is considered overweight. Above 30 is deemed to be obese.)
Apple-shaped figure
Individuals who carry most of their weight in the trunk of their bodies (above the hips) tend to have a higher risk of diabetes than those of similar weight with a pear-shaped body (excess fat carried on hips and thighs). Age
Canadian data for 1996-1997 show that the prevalence rate of diabetes in those 65 and older (10.4 per cent) is three times as high as the rate in those 35 to 64 (3.2 per cent).
Sedentary lifestyle
Being physically active can help reduce weight and improve blood-sugar levels. Impaired Glucose Tolerance
A prediabetic condition in which blood glucose (blood sugar) levels are higher than normal.
Ethnic Ancestry
Being of aboriginal, African, Latin American or Asian ancestry increases the risk of developing of Type 2 diabetes. Risk levels for these groups are between two and six times higher than for Canadians of Caucasian origin.
Source: Public Health Agency
of Canada
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